TreeView optimization with large amount of data

I have a treeview that I put ~4000 objects in. The initial load and fill of my treeview comes from a list of objects, and it takes a LONG time. This is how I fill it : ``` private List<ItemIdPair> m_itemList; public List<ItemIdPair> ItemList { get { return m_itemList; } set { m_itemList = value; } } public void Window_Loaded(object sender, RoutedEventArgs e) { try { ItemList = ItemListParse(); // data from .txt file (NOT the performance problem) ItemList = ItemList.OrderBy(o => o.ItemName).ToList(); ItemTreeView.DataContext = ItemList; } catch(Exception ex) { } } ``` My treeview is bound to my Datacontext in the XAML. I also have a textbox to search the treeview and narrow the results which ALSO has a huge performance hit. It looks like this : ``` public void LoadTree(string search) { try { List<ItemIdPair> items = ItemList.Where(i => i.ItemName.ToLower().Contains(search.ToLower())).ToList(); ItemTreeView.DataContext = items; } catch(Exception ex) { } } ``` any tips on how I can optimize this, or refactor it to give me a performance boost? There's no way that a Treeview should behave this slow.